RO-BER Industrial Robots of Kamen in Germany make gantry robots used in handling systems worldwide. They are specialists in the automation and material flow and goods distribution. When it came to improving the performance of their robots in stacking and palletising applications, they turned to Lenze drive technology. The result was a substantial 30% decrease in the typical cycle times for handling goods.
The robots from RO-BER have proved their worth in high performance handling systems for palletising and de-palletising. They allow coverage of large areas and are able to pick from over-lapping work areas which are typically found in the modern distribution centre. They enable the efficient utilisation of space. Compared to floor mounted robots, gantry designs suit cases where the distances goods need to travel are greater, or the paths are varied, as well as requiring minimal floor space.
The RO-BER gantry robots are robust and constructed with a precise degree of balance. All the moving components are lightened to minimise the inertial loads during acceleration and deceleration. The modular design allows the robots to be adapted for different tasks. Their ability to achieve positioning both dynamically and accurately is a result of the servo drive system.
Lenze synchronous AC servo motors driven by Lenze servo drives achieve a high dynamic response over the whole speed range with delivery of an almost constant torque. High resolution resolvers built into the motors guarantee pin point positioning and high repeatable accuracy.
Load capacities range from 100kg for the FP100 machine up to 300kg for the FP300. The dynamic performance of the servo system achieves short cycle times and adds up to maximum operating performance. In operation noise levels are low. The servo drive system is maintenance free leading to low maintenance requirements for the whole robot together with maximum reliability.
The robots are quick to assemble and the programming and commissioning processes are fast due to the independent axes. Accurate positioning is achieved from a motion controller from Lenze, the model ETC. This combines the advantages of two automation concepts - numerical path control (CNC) and a freely programmable PLC combined into one unit. The ETC controllers are capable of up to 12 axes and can be panel mounted or built into an industrial PC in card form.
Programming the RO-BER gantry robots is particularly easy because the standard G-code language is not only suitable for CNC applications but also for all movements in Cartesian space. With gantry robots, Cartesian movements relate to the X, Y and Z Cartesian axes.
No special robot language is required, not even any transformation for arm rotation. The ETC motion controller uses two CAN interfaces for communication: one for the I / O bus and the other to link to the servo drives. Here a bank of Lenze ECS servo drives obtained their positional information from the drive bus in milli-second clock pulses.
An additional Ethernet TCP / IP communication interface on the ETC controller provides the connection between the drive system and a higher level IPC. Through this interface the PLC can be programmed, product data transferred and current process parameters diagnosed.
So that the customer can programme and gain detailed system diagnostics directly from his PC to the drive, an additional OPC interface enables parameter setting and diagnostics of all nodes connected to the CAN interfaces. With the control software running on a standard industrial PC, all the well known benefits of PC systems can be exploited: data storage on different media, visualisation, programming and networking of computer systems.
Process and load plan data are stored centrally in a database and the data are transferred to the CNC and PLC control units. Robots need to be highly versatile in their movements. The Lenze servo system is especially adapted for multi-axis motions with high overload capacity.
The Lenze ECS servo drives are optimally matched to the Lenze MCS synchronous servo motors. In this application, four axes are controlled by the ECS drives - X, Y, Z (lift axis) and C, which turns the picker arm. RO-BER actually uses several of the systems side by side for the same area gantry. In addition the ECS drives are networked with Lenze 8200 vector inverters to control further axis for moving and positioning conveyors and stackers at the operating station.
The ECS multi-axis drive system consists of several axis units powered from a central supply module, giving the advantage of energy saving. The supply module and axis drives are linked with a common DC bus allowing braking energy from individual axes to be fed back and reused by axes that are in acceleration mode. This reduces the average power requirement and in particular the peak demand.
The common DC bus feature of the ECS drives saves on both cabling and external components such as mains fuses and filters. The ECS servo system is rated for between 2 and 20A per axis with an overload capacity of up to 300%. To ensure that the robots can withstand constant speed variations, acceleration, stops and the vibrations which occurred during the handling operation, motors need to be robust.
Lenze MCS synchronous motors are just that. Thanks to an innovative winding technique where poles are wound individually prior to assembly, they have a higher than usual copper fill resulting in a high power density. The resulting strong magnetic flux allows excellent smooth running even at low speeds with cogging torques almost imperceptible. This aids the positioning resolution of the robot.
A new generation of magnets is resistant to corrosion and demagnetisation, even at high temperatures. Large bearings mean that strong high radial forces can be applied to the shaft without adversely affecting life, so the motors can operate with high radial loads. MCS synchronous motors are available for torques in the range from 0.5 to 190Nm. On these robots they drive the X, Y and Z axes with a further two motors applied to drive the C axis.
All these synchronous servo motors are fitted with a feedback resolver and permanent magnet brakes for holding and emergency stop. Lenze also supplied an external brake resistor and system cables of which the motor and resolver cables are suitable for trailing.
To help RO-BER specify the optimum drive system that would accurately achieve the positioning, Lenze engineers used special software called Drive Solution Designer (DSD). This has been developed to bring together drive knowledge and experience from applications all over the world. It looks at all aspects of the drive considering ambient conditions, static and dynamic loadings, torque and speed capacities to create a time / position profile.
Using DSD the motion sequence for individual drives was optimised, for example by using S shaped acceleration ramps and adding intermittent positioning motions. This reduced load on the drives and the mechanical structure of the robot, leading to smoother handling of the product. The DSD software was one of the key factors leading to the reduction in cycle times in the handling of material.
Commissioning of the RO-BER gantry robots went very smoothly, partly because RO-BER had prior experience with the ETC motion control system. With the new Lenze drives, it took just one-half days to install cabling and set the current control parameters using Lenze Global Drive Control software. A further day allowed all the power measurements, including documentation with various loads, to be completed.
The drive system exceeded the customer specification with capacity to spare on each axis of this multi-axis system. By changing to a Lenze servo drive system, RO-BER achieved performance that exceeded their requirements for dynamics and prec